1. Field of the Invention
The present invention relates to a vibration damping device to be used, for example, for an automobile engine mount, especially to a fluid filled vibration damping device using vibration effects based on the flow behavior of an incompressible fluid sealed therein.
2. Description of the Related Art
Conventionally, as a vibration damping device interposed between the members constituting a vibration transmission system that connects said members to each other or supports them in a vibration-damping manner, there has been known a fluid filled vibration damping device using vibration damping effects based on the flow behavior of an incompressible fluid sealed therein. This fluid filled vibration damping device has a structure where a first mounting member and a second mounting member are elastically connected by a main rubber elastic body, wherein a pressure receiving chamber with its walls partially composed of the main rubber elastic body and a equilibrium chamber with its walls partially composed of a flexible membrane are formed, and further, an orifice passage is formed to connect said pressure receiving chamber and said equilibrium chamber with each other. In addition, in a containing space formed within a partition member that separates the pressure receiving chamber from the equilibrium chamber, a movable member is arranged to which fluid pressures of the pressure receiving chamber and equilibrium chamber are applied via a plurality of through holes penetrating through the walls of the containing space, thus constituting a fluid pressure transmission mechanism that transmits fluid pressure between the two chambers taking advantage of the deformation or displacement of the movable member. For example, the one disclosed in Japanese Patent No. JP-B-4790668 is such a device.
Meanwhile, it is feasible to seal the incompressible fluid in the pressure receiving chamber and the equilibrium chamber, for example by carrying out the forming process of the pressure receiving chamber and the equilibrium chamber within a water tank filled with the incompressible fluid, but as shown in JP-B-4790668, the incompressible fluid is sometimes sealed in the pressure receiving chamber and the equilibrium chamber after the formation thereof. In such a post-formation filling type fluid filled vibration damping device, a communication passage is formed that connects the pressure receiving chamber and the equilibrium chamber with the exterior space, wherein the incompressible fluid is poured into these pressure receiving chamber and equilibrium chamber after air therein is forced out via the communication passage.
However, if one tries to force out (vacuum draw) air in the pressure receiving chamber and the equilibrium chamber via the communication passage, the inner pressures of the pressure receiving chamber and the equilibrium chamber drop down so that the flexible membrane made easily deformable is adsorbed to the side of the partition member. Especially, according to the structure of JP-B-4790668, the communication passage is open to the pressure receiving chamber by which air in the equilibrium chamber is let out via the orifice passage. Therefore, the flexible membrane is quickly deformed around the opening of the orifice passage on the side of the equilibrium chamber to cover such opening, thus posing a risk of residual air remaining in the equilibrium chamber.
In addition, once any opening of the through holes on the equilibrium chamber side is covered with the flexible membrane under the condition where the through holes penetrating through the walls of the containing space on the side of the pressure receiving chamber are blocked because the movable member is adsorbed to the inner wall of the containing space on the side of the pressure receiving chamber due to the negative pressure thereof, the space between the opposing faces of the movable member and the flexible membrane is sealed off. As a result, air can be trapped within the sealed through holes, which can pose a risk of air being led to the liquid chambers to cause its compressibility to adversely affect the vibration damping properties.